Spring holder



Feb. 11, 19 58 H. c. REYNOLDS SPRING HOLDER Filed Dec. 27, 1955 'mveuroRHAROLD C. REYNOLDS M HIS ATTORNEYMI I FIG I SPRING HOLDER Harold C.Reynolds, Athens, Pa., assignor to Ingersoll- Rand Company, New York, N.Y., a corporation of New Jersey Application December 27, 1955, SerialNo. 555,666

6 Claims. (CI. 64-15) This invention relates to spring holders, and moreparticularly to an adjustable device adapted to hold a torsion spring inany one of a number of positions of pretension.

It is one object of this invention to provide a spring holder which isrelatively simple in construction and easily adjustable to obtainvarious degrees of tension of the spring held thereby.

A second object of the invention is to provide such a holder in whichthe degree of stress of the spring may be easily determined.

Another object of this invention is to provide such a spring holder inwhich relatively fine adjustment of the degree of tension of the springis obtainable.

Other objects of the invention will become obvious from the followingspecification and attached drawing in which- Figure l is a longitudinalsectional elevation showing an impact tool, in part, to which the springholder is adapted,

Figs. 2 and 3 are cross sectional views of Fig. 1 taken along the lines22 and 33, respectively, looking in the direction of the arrows, and

Fig. 4 is a perspective view looking at one end of the spring holder.

Referring to the drawings, and particularly to Fig. l,

a preferred embodiment of the spring holder is shown adapted to atorsion type spring having a splined portion 12 at its outer end. Thespring holder comprises, in general, a member 14 engaged to the innerend of the spring against rotation relative thereto and having a splinedportion 16 at its opposite end. The spring is placed under stress byrotating the splined end portion of the spring and at the same timeholding the member 14 against rotation. When the desired degree ofstress is obtained, a coupling element 18 is positioned on the spring 10and member 14 with splined portions 20 and 22 engaging the correspondingsplined portions 12 and 16 on the spring 10 and member 14, respectively.

It is to be noted that this splined connection is such that limitedmovement of the spring 10 relative to the member 14 is permitted. Inorder to fully understand the purpose of this detail of the invention,the spring holder and spring are shown adapted to a conventional rotarytype impact tool commonly used for rotating screws, nuts and the like.The particular impact tool shown, in part, is fully described in U. S.Patent No. 2,160,150. This tool comprises, in general, a continuouslyrotated motor driven spindle 24 connected through a ball-cam 26-28 torotate a hammer 30. The hammer 30 is provided with a pair of dependingjaws 32 arranged to engage a pair of similarly constructed jaws 34mounted on the member 14, which in the embodiment of the inventiondisclosed serves additionally as the anvil of the impact tool.

The operation of the tool is such that the hammer is held in engagementwith the anvil by a spring 36 whenever the resistance to rotation of theanvil is below a predetermined value-for example, the run down portionof nite States Patent-O "ice mitted by the anvil directly to the work.In the construction shown, however, a spring is interposed between theanvil and the work. It is to be noted that because one end of the springis engaged to the work, whenever a turning force is applied to theopposite end by the anvil there is a tendency for the spring to be woundup and hence move the work end of the spring relative to the anvil.

In order to avoid this action when the work is'below a predetermineddegree of tightness, the spring is placed under tension, or stress, in adirection opposing relative rotation between the spring 10 and the anvilmember 14. Accordingly, until the rotational force of the hammer exceedsthe pretensioned force of the spring, the spring acts as a substantiallyrigid element. When this force exceeds the pretension of the spring,then the spring is further tensioned by the action of the anvil. Theenergy of this excess force is accumulated by the spring and thereafterreturned to the hammer in accentnating the rebounding thereof. In thisway the amount of torque transmitted to the work is limited to thedegree of pretensioning of the spring. 7

In order, however, that the spring may be further tensioned by the anvilto accomplish the result specified, it is necessary that the splined endof the spring be free to move relative to the member 14, and it is forthis reason that the spring holding device is designed to permit suchlimited relative rotation.

Referring now to the structural details of the spring holding deviceshown, the spring disclosed is cruciform in cross sectional form and isprovided at one end with a square 38 fitted in a square socket 40 in themember 14. The member 14 is substantially tubular in shape encirclingthe spring 10 and extending therealong to the splined portion 12 of thespring. 7

The .coupling element 18 is in the form of a tubular element havingsplines and grooves 46 and 48 corresponding in size and number to thesplines and grooves 42 and 44 of the member 14 such that there is arelatively tight fit therebetween whenever the coupling element is inits assembled position as shown in Fig. l.

The opposite end portion of the bore of the coupling element 18 issomewhat reduced in diameter and is formed with splines and grooves 54and 56 equal in number to the splines and grooves 50 and 52 of thespring 10 and adapted to receive this portion of the spring. it is to benoted, however, that the grooves 56 in the coupling element 18 aresubstantially greater in width than the width of the splines 58 of thespring (see Figs. 3 and 4), and the grooves 52 of the spring are ofsubstantially greater width than the width of the splines 54 of thecoupling element so as to permit limited relative rotational movementbetween the spring and the member 14 for the reasons specifiedhereinbefore.

It will be noted further that the number of splines 42 of the member 14are equal to the number of splines 46 of the splined portion of thecoupling element 18 received thereby but are not equal to the number ofsplines 50 of the splined portion of the spring 10 or the associatedsplines 54 of the coupling element 18.

The reason for providing this unequal number of splines on the springand the member 14 is to obtain a greater number of engaging positions ofthe element 18 with the spring and the member 14 for 360 of revolutionof the spring, the coupling element 18 and member 14 being heldstationary, than is possible if an equal'numher of splines were used. Inother words, if the number of splines on the spring and the member 14were equal, then it is clear that in order to rotate the spring 10 fromone position to the next at which the coupling element can be mounted,the spring would have to be rotated through a number of degreesdetermined by the equation-360 divided by the number of splines. In thepresent invention this number of degrees of movement of the springbetween engaging positions of the coupling element is reduced to obtaina finer degree of adjustment of the spring by providing a greater numberof splines on the member 14 than on the spring. The number of degreesbetween engaging positions of the coupling element 18 is determined bythe equation Another advantage of this construction is that a fewernumber of splines may be placed on the relatively small diameteredspring and thus the size of the splines may be maintained suflicientlylarge to withstand any stress or hammer action to which they aresubjected during the operation of the tool or other apparatus with whichthe spring is associated.

Utilizing the above equation and knowing the spring constant of thespring 10, the amount of stress applied to the spring in moving from oneengaging position to the next may be readily calculated. For example, ifthe spring is rotated 10 between each engaging position of the couplingelement and the spring has a constant of six foot pounds per degree,then it is clear that the spring is stressed sixty foot-pounds betweeneach engaging position of the coupling element 18.

In order that the operator assembling the spring in a pretensioned statemay readily determine the number of engaging positions through which thespring is rotated and hence determine the approximate degree of tensionof the spring, an index mark 58 is placed on the spring to indicate theposition of one of the spring splines 50 and index marks, as for example1-14, are provided to indicate each of the grooves 56 of the couplingelement 18.

I claim:

1. A device for holding under stress a spring having :1

grooved and splined end portion, comprising a member engaged to theother one end portion of the spring against relative rotary movement andhaving a grooved and splined end portion adjacent said splined end ofthe spring, and a coupling element having a splined and grooved portionadapted to receive the splines on said member and a second splined andgrooved portion adapted to receive the splines on said spring, thegrooves in the first said splined portion of said element are ofsubstantially greater width than the splines of the spring so as topermit limited relative rotation between the splined end portion of thespring and the associated end of said member.

2. The device claimed in claim 1 in which the number of splines on thespring is difiierent than the number of splines on said member.

3. The device claimed in claim 2 in which an index mark is provided onthe spring and marking is provided on said member to show the angularrelation therebetween.

4. The combination of an elongated torsional spring having an externalsplined portion at one end section thereof, a tubular member encirclingsaid spring and positively engaged to the opposite end section of saidspring against relative rotation in either direction, said memberterminating at one end adjacent said splined portion of the spring andhaving external splines on the periphery of said end, and a tubularcoupling element adapted to be positioned to encircle the splinedportions of the spring and of the tubular member and having internalsplined portions constructed to mate with the splined portions of thespring and of said member.

5. The device claimed in claim 4 in which there is a greater number ofsplines on said member than on the spring.

6. The device claimed in claim 5 in which there is a loose fit betweenthe connecting splined portions of the coupling element and said spring.

References Cited in the file of this patent UNITED STATES PATENTS1,884,029 Luyks Oct. 25, 1932 2,250,736 Torresen July 29, 1941 2,527,517Barker et al Oct. 31, 1950

